The broad objectives of the proposed research are to provide experimental evidence to distinguish the role of aging from the possible additional role of obesity on age-related alterations in selected tissue metabolic functions, hormone binding by tissues and on hormonal responsiveness. The investigations proposed will include the following objectives: Topic 1) To develop and characterize a model of aging in 4 groups of rats in which the degree of adiposity will be controlled by dietary regulation (ad libitum feeding, and 80%, 60% or 40% of ad libitum ration) from age 3 to 24 months; Topic 2) To study in each group of animals the effects of aging (3 vs 6, 12, 18 and 24 months) on adipose tissue cellularity, glucose transport and metabolism, basal lipolysis, hormone binding by adipocytes and their responsiveness to insulin and lipolytic hormones. The effects of aging on selected extraadipose metabolic processes and hormonal regulation will be studied; Topic 3) To compare in animals of similar age the alterations in the above described parameters that may be produced by obesity alone. In most mammalian species fed ad libitum, aging is accompanied by progressively increasing adipose mass. The experimental design proposed should allow a separation of the aging effect from the obesity effect on cell functions, by carefully comparing cells of different size in animals of similar age, and also cells of comparable size in animals of different age. In animals exposed to caloric restriction, careful efforts will be made to deliver allotted food portions with minimal or no disruption of the periodicity of food intake.